SpaceX’s Falcon Heavy rocket, now on the launchpad at Kennedy Space Center in Florida, has suffered another setback in its long-awaited development. A critical engine test fire, originally scheduled for earlier this week, has been pushed back to Monday afternoon and evening. While the Heavy’s core stage was successfully tested last year, this marks the first test of the fully assembled rocket under launch conditions. Vapors were seen trailing upward from the launch pad Thursday and Friday, confirming the rocket had been fueled in preparation of the test.

The test fire, which involves igniting all 27 of the rocket’s engines for twelve seconds of maximum thrust, was repeatedly delayed for unknown reasons.

Eventually, however, NASA personnel cited SpaceX for failing to test the engine in the allotted time; the company failed to perform the test before a scheduled launch of a United Launch Alliance (ULA) Atlas V rocket from neighboring Cape Canaveral Air Force Station. The ULA Atlas, carrying a missile-detecting satellite as part of the US Air Force’s Space-Based Infrared System (SBIRS), successfully lifted off Friday evening.

Test future uncertain with government shutdown

The news of the test delay comes on the heels of the US government shutdown. NASA procedures in the event of a shutdown continue to operate crucial programs such as the International Space Station, but many employees will be furloughed. According to NASA officials, only those employees whose work is deemed critical to protecting the health and safety of humans or property will be exempt from the furlough.

While the Falcon Heavy is private property, Kennedy Space Center is operated by NASA personnel. However, SpaceX has publicly stated it does not expect the shutdown to interfere with its operations.

An unusual payload

Most rockets, during test flights, carry blocks of steel or concrete as simulated payloads—to determine how the rocket will fly with the extra weight. SpaceX founder and CEO Elon Musk, however, has other ideas. In an Instagram post, he confirmed that the Falcon Heavy’s first operational payload will not be concrete or steel, but his own cherry-red Tesla Roadster [VIDEO]. In a tweet, he expressed amusement at the thought of aliens one day discovering an orbiting sports car. It is a whimsical, showman-like, and very Muskian move.

The Falcon Heavy, by the numbers

The rocket’s 27 engines, at full thrust, will produce a total 5.13 million pounds (or 22,819 kilonewtons) of thrust.

It will be, by all accounts, the most powerful launch from Cape Canaveral since the final launch of the Saturn V rocket in 1973. When the Heavy is declared fully operational, it will be (according to the company) the most powerful rocket in the world, capable of lifting over 140,000 pounds (64,000 kilograms) to Low Earth Orbit (LEO). Moreover, three of SpaceX’s workhorse Falcon 9 cores comprise the first stage, designed to be reusable. SpaceX has already demonstrated (after numerous failures) that its Falcon 9 can land remotely and be reused, greatly decreasing the Falcon Heavy’s operational costs.

Launch dates remain unchanged

Even with the setback, Musk still hopes to successfully launch the Falcon Heavy before the end of January, despite not releasing a set launch date. Even acknowledging the risk of failure (to which he is no stranger) it’s a prudent decision to remain cautious. The Falcon Heavy will not only be the most powerful rocket the company has launched, but also the most technically complicated. But if this upcoming engine test leads to a successful test flight later, it will mark a new chapter in private spaceflight.